1. Field
Various features pertain to broadcast control channels. At least one aspect pertains to methods for protecting a multiple message broadcast control channel.
2. Background
In a wireless multicast or broadcast delivery system, content and control information are transmitted from a single network server to several recipients over a lossy transmission environment, i.e., a wireless multicast channel. The control information typically includes two types of messages, a single primary message and one or more secondary messages. The primary message contains information that is processed by every recipient. It contains global information about the transmission network and includes identification information about the secondary messages, i.e. secondary messages identifiers. Therefore, the primary message is typically processed by the recipients before any of the secondary messages can be processed.
Secondary message includes data blocks, that is, a number M data blocks, which contain information that only a subset of the N recipients actually process. For example, the secondary messages may be addressed to a subset of all the recipients while the data blocks may be targeted for one or more recipients within the subset. The secondary messages may also be processed by every recipient or by only some of the recipients. The data blocks may also be processed by all or only some of the recipients.
It is possible for the recipients to receive erroneous information from these messages. Noise from the transmission media may alter the contents of the primary and/or secondary messages. Also, interference, such as intentional interference by malicious parties attempting to interfere with the communications may alter the primary and/or secondary messages. In most communication systems, the underlying communication infrastructure applies error-correcting codes to a whole message that can correct many, but not all, transmission errors. However, the error-correcting codes are able to detect the uncorrectable errors. In this case, the data blocks with uncorrectable errors are treated as erasures, and the corresponding data is ignored by the recipients.
While corrupted, erroneous or tampered data blocks (e.g., containing video, audio, etc.) may cause some information to be presented incorrectly or incomplete, its malicious effects are relatively limited. However, if blocks containing control messages are modified or tampered in transit (e.g., by a malicious entity), these control messages can potentially change or modify the operation of the receiver device (e.g., change codes, channels, security levels, etc.) thereby compromising its operation and/or security. In such scenarios, it is the goal of an attacker to cause the recipients to process these modified control messages, thereby changing the receiver's state of operation to a malicious state. Consequently, a method is needed to efficiently protect a multi-part broadcast control messages during transmission and/or be able to ascertain whether a control message has or has not been modified.